The present invention relates to continuously monitoring the function of nuclear radiation measuring channels.
Nuclear reactors are extensively equipped with measuring and protective equipment and combinations thereof. Such equipment includes, for example, multiple radiation detection and measuring channels, each having an ionization chamber. A typical channel is for example provided for measuring the power of the reactor for various reasons, last but not least for reasons of safety. Such a measuring channel must be quite reliable and, therefore, its proper functioning has to be supervised.
Ionization chambers used for measuring nuclear radiation are, for example, disclosed in principle as well as in regard to circuit details in "Strahlung und Strahlungsme.beta.technik in Kernkraftwerken", Elitera 1974, pages 118, 119, FIGS. 3/1, 3/2, 3/3. Ionization chambers of that type are, for example, disposed in between the fuel element bundles in the core of the reactor. The ionization chambers operate in principle in that they detect the electric current resulting from the movement of ions produced by the nuclear radiation. This current is used as a criterium for the intensity of the radiation to be measured.
Considering a measuring channel, only the ionization chamber thereof being so to speak the front-end element, is exposed directly to the radiation. Accordingly, electrical conductors and cables are run between that ionization chamber in the reactor core and e.g. a console, panel or display board. These cables are, for example, insulated with a ceramic material. It is inherent that at least a portion of that cable is subjected extensively to nuclear radiation. Also, the thermal load on these cables is quite high. It was found that on a long term basis, these thermal and radiation load conditions reduce the insulating resistance of the cable. Also, such ceramic insulation is quite sensitive against penetration of moisture; already very small quantities of moisture penetrating the ceramic reduces drastically the insulative strength of that cable. The invention is not concerned with cable engineering, but is based on cognizance of these conditions and problems.
It was observed that these various interferences produce a leakage current in the cable which may become as large as the signal and measuring current from the ionization chamber so that, on one hand, these currents are no longer distinguishable and on the other hand, the measured resultant current is quite incorrect. It can readily be seen that particularly for reasons of safety such a condition is intolerable.
The literature citation introduced above mentions particularly on page 172 test equipment generally for recognizing dangerous operating conditions. This test equipment includes particularly insulation measuring devices. However, they include inherently high voltage components and DC amplifier units and such components are quite expensive and occupy significant amounts of space.